You almost certainly know at least one infuriating person who is what I'll call, for want of a better term, a life-choice evangelist. As the label suggests, LCEs are driven by the anxious insistence that whatever major decisions they've made – to get married, to have or not have kids, to sacrifice fulfilling work for a higher salary, or vice versa – are best for everyone. If he's married, an LCE will seem unable to comprehend why anyone wouldn't choose to be; if she's single and you're not, she'll drop hints that you should envy her freedom. Contradict an LCE, by suggesting an alternative life path, and you'll witness a face flicker of confusion, as if you might not be speaking English. If you really know nobody like this, then I'm afraid it's probably you. One simple test: at a wedding reception, have you ever, with aggressive joviality, asked an unmarried couple when they're going to tie the knot? Thought so.

The LCEs' real motivation, you suspect, isn't their certainty that marriage, or parenthood, or leaving the city for the country, would be best for you. Rather, it's that they worry, perhaps subconsciously, that it's not best for them: their efforts to persuade are an attempt to reassure themselves. A study soon to be published in Psychological Science strongly suggests that's so. The Stanford researcher Kristin Laurin and her colleagues found that people think more highly of those with the same relationship status as them – even when it shouldn't matter, as when hiring someone for a job, or deciding which politician to vote for. In one exercise, participants were asked, on Valentine's Day, to imagine how a hypothetical character, "Nick" or "Nicole", would experience that evening. Nick/Nicole was sometimes described as single, sometimes as coupled – and people consistently predicted a happier Valentine's for the one who shared their own status.

The truly telling detail, though, was that the effect was more marked the more permanent people believed their own status to be. It wasn't the most happily coupled-up people who thought coupledom was best; it was those who thought their position least likely to change who most strongly felt it was preferable for all. "Perceiving an unchangeable situation as undesirable can lead to feelings of being 'trapped'," the researchers write. One way to avoid that "is to represent one's current situation as an ideal – not just for oneself, but universally." If marriage is best for everyone, the logic goes, it must be best for me.

Life-choice evangelism, then, looks like a classic response to cognitive dissonance: when there's a clash between your situation (being single or coupled) and your belief (being unsure about whether that situation is right for you), it's often easiest to modify the belief. It's tempting to see this as self-deception, and therefore bad. But self-help types are always urging us to "want what we have", and as long as you're not, say, in an abusive relationship, what's wrong with persuading yourself life's great? The problem arises when you try but don't succeed: the most annoying LCEs, after all, are those who seem least convinced by their own argument. Which suggests a novel solution: next time you're collared by one, just agree enthusiastically. You'll be doing the LCE a favour; he or she will think the favour's the other way around. Both of you get to feel superior. How's that for a result?